Field of the Invention
The present invention relates to a display device, especially to a display device capable of improving the efficiency in guiding light downward.
Description of the Related Art
Front light modules for transflective or reflective displays are commonly of edge-lighting type or direct-lighting type, wherein the front light modules of edge-lighting type are becoming dominant due to the market's growing demand on small form factor of displays.
A typical front light module of edge-lighting type generally installs a downward-light-guiding means on the top face of a light guide plate, to transform an edge light to a uniform plane light, which emits light beams downward to provide illumination for a display. Please refer to FIG. 1, which illustrates a cross sectional view of a front light module for providing a plane light to illuminate a reflective type LCD 140 according to a prior art. As illustrated in FIG. 1, the front light module includes a light source 100, a reflective cover 110, a diffusion plate 120, and a light guide plate 130.
In the module, the light source 100, reflective cover 110, and diffusion plate 120 are used for providing diffused incident light.
The light guide plate 130, of which the left side face is a light entrance surface close to the diffusion plate 120, the bottom face is a light exit surface, and the top face has a plurality of diffusion points 131, wherein, the diffused incident light hitting the diffusion points 131 indirectly (after going through a total reflection at the bottom face of the light guide plate 130) or directly will be scattered off, and some of the scattered light—of which the traveling direction forms with a normal line of the light exit surface an angle smaller than a total reflection angle—will pass through the light exit surface to illuminate the reflective type LCD 140.
Although the diffusion points 131 have the advantage of easy implementation (can use sand-blasting process), however, the efficiency in guiding light downward is not good enough—some of the light scattered by the diffusion points 131 will emit away from the top face of the light guide plate 130, causing energy loss.
To improve the efficiency in guiding light downward, there is another prior art design using microstructure as a means for guiding light downward. Please refer to FIG. 2, which illustrates a cross sectional view of a front light module for providing a plane light to illuminate a reflective type LCD 240 according to another prior art. As illustrated in FIG. 2, the front light module includes a light source 200, a reflective cover 210, a diffusion plate 220, and a light guide plate 230.
In the module, the light source 200, reflective cover 210, and diffusion plate 220 are used for providing diffused incident light.
The light guide plate 230, of which the left side face is a light entrance surface close to the diffusion plate 220, the bottom face is a light exit surface, and the top face has a plurality of V type microstructures 231, wherein, the diffused incident light hitting the V type microstructures 231 indirectly (after going through a total reflection at the bottom face of the light guide plate 230) or directly will be reflected to travel down along a normal line of the light exit surface to pass through the light exit surface to illuminate the reflective type LCD 240.
Although the V type microstructures 231 can provide better efficiency in guiding light downward, nevertheless, they have the disadvantage of being not easy to implement.
What is more, as the diffusion points 131 of the front light module of FIG. 1 and the V type microstructures 231 of the front light module of FIG. 2 are located at the top face of the light guide plate, therefore they both have the problems of interfering with a user's viewing the display and being subject to getting scratched.
In view of the foregoing problems, the present invention proposes a front light module having a novel structure for guiding light downward.